Such a carriage for a stretcher is known from U.S. Pat. No. 4,921,295. While the front legs at the front end or the frame have fixed, i.e. unpivotable castors (rollers), the rear legs are provided with pivotable steering rollers so that the carriage may be guided while being pushed. In order to bring a patient in shock into an appropriate position on the stretcher while moving the latter by means of the carriage, the front legs may be locked at the frame in at least two pivotal positions by means of disengagable locking device. In the one pivotal position, the front legs are pivoted down completely; this position is usually taken by the front legs when the carriage is moved. Additionally, the front legs may be locked in a second pivotal position wherein their angle to the frame is more acute than in the first position so that the front end of the carriage is lowered as necessary for positioning persons in shock.
Although the known carriage is provided with steering rollers, its maneuverability is limited. In narrow halls full of nooks and crannies, moving the carriage is difficult since a steering only by the rear steering rollers is not sufficient at narrow corners. Further, a lateral displacement of the carriage is impossible without a troublesome moving of the carriage back and forth and without maneuvering or lifting the same. When lifting the carriage, there is the danger that the patient is subjected to painful vibrations.
If the front rollers were replaced with pivotable castors, the carriage could hardly be controlled, if at all, when being moved on sloping surfaces. Further, the trailing necessary with guide rolls (i.e. the vertical pivot axis of the steering rollers lies ahead of the horizontal rotational axis of the steering rollers with respect to the direction of movement) would be disadvantageous when lowering the front end since, with the front legs inclined, the own weight of the carriage would exert a rotational moment on the steering rollers that would result in an undesired rotation of the steering roller about the pivot axis and keep the guide rollers in their forward movement position.
On the other hand, the castors at the front legs have to be designed unpivotable since it is necessary to be able to move the carriage exactly onto the loading platform of an ambulance. The solution of this problem, providing each front leg with a castor that may be locked in the forward position, is not practicable since the rotational moment, caused by the trailing of the steering rollers when the front end is lowered, would exert extremely great forces on the lock of the steering rollers, which would result in a rather high wear.